Typical gas turbine engine fuel supply systems include a fuel source, such as a fuel tank, and one or more pumps that draw fuel from the fuel tank and deliver pressurized fuel to one or more primary fuel loads and to one or more secondary fuel loads via one or more supply lines. Generally, the primary fuel loads, which include the fuel manifolds in the engine combustor, are supplied with fuel via, for example, a priority flow line, and the secondary fuel loads, which may include a motive flow valve and regulator, one or more variable geometry actuators, and one or more bleed valves, are supplied with fuel via, for example, a secondary flow line.
During some operational conditions, the total fuel demand of the primary and secondary loads may be at or near the delivery capacity of the one or more pumps that deliver fuel to the loads. This can result in decreased fuel flow to both the primary and secondary loads. In the case where the primary fuel load is a gas turbine engine combustor, this reduced fuel flow can lead to undesirable effects, such as engine flame out or inability to start the engine. Thus, many fuel delivery systems are configured to either inhibit or prohibit fuel flow to secondary fuel loads when fuel demand is at, or approaching, pump delivery capacity. For example, many fuel delivery systems include one or more function-specific valves that are configured to prohibit fuel flow to the secondary fuel loads when fuel demand is at, or approaching, pump delivery capacity.
Although the above-described configuration is generally safe and reliable for prohibiting fuel flow to secondary fuel loads when needed, it does suffer certain drawbacks. For example, it is typically used only during an engine start sequence, and may not be active during other operational configurations of the engine. Additionally, because it uses function-specific valves, it can result in increased system weight, cost, and pressure drop, and can further result in decreased overall system reliability. Hence, there is a need for a system that prioritizes flow to a plurality of loads, such as primary and secondary fuel loads, and that provides a relative decrease in overall system weight, cost, and pressure drop, and/or can increase overall system reliability. The present invention addresses one or more of these needs.